There are conventional methods for controlling combustion of an internal combustion engine in a vehicle and the like by controlling the spray amount of the fuel so as to match the amount of air sucked from the atmosphere, igniting a mixture of air and fuel in accordance with the angle of rotation of the crank shaft, and injecting it (e.g., see Japan Examined Patent Application, Second Publication No. H04-15388).
The abovementioned document discloses a technique for controlling fuel injection. Specifically, an air flow sensor is used for controlling injection of fuel to a multi-cylinder engine, and is provided in an air intake passage between a throttle valve and an electromagnetic injection valve. A control circuit calculates a basic injection amount from the average flow of inlet air which is measured by the air flow sensor, and the fuel is injected based on this basic injection amount. While the engine cylinder which inlets air changes sequentially in each cycle, fluctuation in the air inlet flow arising at this time is treated as deviation from the average flow of inlet air, and a deviation signal which corresponds to this deviation is directly input to a voltage circuit of the electromagnetic injection valve. More fuel is injected when the deviation signal is large, and less fuel is injected when the deviation is small. The basic injection amount is calculated by compensation using an air inlet temperature sensor which measures the temperature of inlet air, and a cooling water temperature sensor which measures the temperature of cooling water in the engine.
To increase the combustion efficiency and responsiveness, the amount of air actually sucked by the internal combustion engine should be measured in each case, and the optimal amount of fuel determined accordingly. However, when measuring the air flow near the throttle valve, disruption of the air stream caused by opening and closing the throttle valve makes it impossible to accurately measure the flow of air. On the other hand, since the air flow changes little at positions away from the throttle valve, it is difficult to measure changes in the air flow caused by the inlet stroke. In this case, the start and end of air suction must be confirmed by combined use of a sensor for measuring the angle of rotation of another crank shaft, a sensor for measuring the angle of rotation of the cam, and the like. This leads to problems in that, when the number of sensors required to control the injection of fuel increases, processing becomes accordingly complex and the load of the control circuit increases.
The present invention has been realized in order to solve the problems mentioned above by providing a control system for internal combustion engine which has a simple constitution and can inject the required amount of fuel at an appropriate timing.